High-priced defensive end Mario Williams is feeling the heat more than he's been applying it four games into his first season with the Buffalo Bills.

As for his production, 1½ sacks, 11 tackles and a fumble recovery, Williams acknowledged he has to do better.

The two-time Pro Bowl selection isn't anywhere near the dominating form he had during his six seasons in Houston, where he set a franchise record with 53 sacks. That was the kind of production the Bills were counting on in March, when they made Williams the NFL's most expensive defensive player by signing him to a six-year, $100 million contract.

Four games in, the Bills (2-2) are preparing to play at San Francisco (3-1) with a defense that's been inconsistent at best and is coming off a monumental collapse in a 52-28 loss to New England.